We have an Interphase Probe, a model almost ten years old now. Interphase: Manufacturer of Forward Looking Sonars, Navigational Chart Plotters, WAAS/GPS and Fish Finders
I don't think that's being made now, but newer units certainly are, including a "black box" that will send info to most chart plotters.
Our Probe scans (no moving parts
so has been completely trouble-free) from the level of the transducer, parallel to the water
surface, to directly below the boat: a 90° view. The beam can also be steered: quite useful in ice since the water
behind a sunken terminal moraine is usually quite deep. We can "see" about 1200 ft in front of the boat, and 800 feet down. Glacial water usually has a lot of ground-up mountain in it so has a lot of particulate: getting to 800 ft will not happen. The thermoclines (layers of dramatically different water temps) also bounce sonar off and can drastically limit the usefulness of any sonar. Be careful out there!
[I bought the Interphase when a friend told me his story. His newly installed Probe sounded an alarm
for a danger
ahead, although he could not see anything. He slowed anyway, and swerved. The Probe had "seen" a submerged cargo container that had dropped from a container ship! It was just awash so virtually invisible. Since it was a very large steel
box, we're sure that it saved his boat. I bought one that season and it has changed our sailing. Up here, things are not as well charted as in the rest of the US: stone pillars (reaching up to near-surface from very deep water) are not charted at all or are charted out of place. There's an island in Prince William Sound that's 1/4 mile out of place on the chart. In addition, the land is still rebounding from the glaciers so charted depths are wrong by quite a bit. Some areas are not charted at all since they are recently out from under glaciers! Up here, water is usually 1000 ft deep, but it changes quickly.]